The field of the invention relates generally to sensor systems and, more particularly, to optical sensors used with turbomachines.
At least some known turbomachines, such as gas turbine engines, include a plurality of rotating turbine blades or buckets that channel high-temperature fluids through the gas turbine engines. Known turbine buckets are typically coupled to a wheel portion of a rotor within the gas turbine engine and cooperate with the rotor to form a turbine section. The turbine buckets are typically spaced circumferentially in a row extending about the rotor. Moreover, known turbine buckets are arranged in axially-spaced rows that are separated by a plurality of stationary nozzle segments that channel the fluid flowing through the engine towards each subsequent row of rotating buckets. Each row of nozzle segments, in conjunction with an associated row of turbine buckets, is usually referred to as a turbine stage and most known turbine engines include a plurality of turbine stages. The arrangement of turbine buckets and nozzle segments is referred to as a hot gas path.
Such known turbine buckets and nozzle segments in the hot gas path may wear over time. For example, such hot gas path components may exhibit stress-related cracking, such stresses induced by temperatures at or above predetermined parameters. Therefore, many known gas turbine engines include temperature monitoring systems that provide operational temperature data in real time, i.e., at the time of measurement. At least some of these known temperature monitoring systems use optical instruments, e.g., optical pyrometers that generate a voltage output signal representative of the temperatures of the components being monitored. Also, many known gas turbines monitor and record such temperature data as an input to adjust operation, e.g., the firing rate of the gas turbine engine, i.e., the rate and/or ratio of fuel and air being combusted in the engine. In some cases, the temperature data may be used as an input into certain protective features of the engine.
In most known gas turbine engines, soot is a common byproduct of the combustion of hydrocarbon fuels and soot particles may become entrained in the hot gas being channeled through the hot gas path. Such soot particles may have temperatures greater than the components in the hot gas path. The soot particles can contact the optical pyrometers and induce a short burst of voltage signals having an elevated amplitude at the pyrometer output. Many gas turbine engine controllers receive these signals a primary inputs into the associated combustion control features. Therefore, such high voltage signals may be misinterpreted as elevated component temperatures by the combustion control features programmed within the controllers. Specifically, the rate and/or ratio of fuel and air being combusted in the engine may be adjusted due to the erroneous signals. Such conditions may result in an undesired reduction in power production by the turbine and oscillations of power production due to periodic and/or routine soot attachment to, and removal from, the optical pyrometer. Furthermore, the associated temperature indications may be used as an input to the protective features of the gas turbine engine, and an erroneous temperature indication may be significant enough to initiate an unplanned shutdown of the gas turbine engine, i.e., a unit trip.